Judging by our research at Jackson and Milan along with over sprays last week we are seeing more burn of both soybeans and cotton with over the top herbicide applications. In soybeans it is not uncommon to see 20 to 35% burn with herbicides like Blazer, Cobra and fomesafen products. Even Liberty on Liberty Link soybeans is showing about 10 to 15% injury with applications last week. On the cotton side Sequence is showing about 15 to 20% burn in our research. Glufosinate on WideStrike cotton has been very hot. In our research and in a few over sprays brought to my attention injury have been in the 20 to 30% range. WideStrike cotton where Dual was tankmixed with glufosinate an sprayed on cotton injury was even higher ranging from 35 to 45%. Liberty on Liberty Link cotton has been the one bright spot as I have yet to run across any burn from Liberty on this cotton.
Why are we seeing so much foliar burn this spring with these herbicides? The one main answer to this question has been the saturated soil conditions and high relative humidity. Rest assured when we are spraying across these muddy fields the humidity is high which makes herbicides like Liberty more active. Moreover, the cuticles on cotton and soybean leaves are paper thin as a response to all this water which makes them more susceptible to injury. On the positive side, Palmer amaranth control is better under these conditions.
Judging by the early results this year one should approach spraying glufosinate on WideStrike cotton with caution. Every time glufosinate is applied to WideStrike cotton it will injure it. However, in research from GA, TN, NC, MS, AR and LA that injury has rarely translated into yield loss. One of the times, in this research, it did reduce yield some was on heavily thrips injured cotton. Of course, we have a lot of cotton that is heavily stressed by thrips this spring so the decision comes down to weighing the potential injury from glufosinate to the yield loss from Palmer amaranth competition.
In a study Scott Stewart conducted a couple years ago cotton without an insecticide seed treatment was allowed to be injured by thrips and then sprayed with glufosinate and glufosinate tankmixed with three different insecticides on 2 leaf cotton. In this test he lost about 11% of the yield when comparing the glufosinate application alone to Sequence on the thrips stressed cotton. Recent research from Georgia shows that just one Palmer/sq yard will reduce cotton yield by 50%. So it comes down to getting eyes on the field to determine the extent of the Palmer infestation. If it is just a couple spots of Palmer and maybe a few scattered then spray glyphosate plus a residual and chop or otherwise destroy the pigweed in those areas. If the Palmer infestation is much more robust then the down side of yield loss, that may or may not happen, with glufosinate on WideStrike cotton will be more than offset by the 100% guarantee of extensive yield loss from Palmer amaranth competition.
The next question from growers is should they tankmix a residual herbicide, AMS or insecticide in with glufosinate on WideStrike cotton? I would NOT add Dual Magnum in with glufosinate on Widestrike cotton particularly if it has been stressed by thrips. A better approach is to wait a few days and spray a residual herbicide. I would also not add any AMS. It will likely not improve weed control and very likely increase cotton injury. The insecticide is a different story. We have not seen acephate increase injury of glufosinate on Widestrike cotton and with the thrips pressure in many fields this year it probably is warranted.
For the cotton that is Liberty Link or Glytol Liberty Link, which have much better glufosinate tolerance than WideStrike cotton, the decisions on managing GR Palmer is easier. I would spray the cotton as quickly as possible with glufosinate and tankmix in something like Dual Magnum for residual control and insecticide for thrips if needed.
